title: Afferent sensory mechanisms involved in jaw gape-related muscle activation in unilateral biting.
abstract: OBJECTIVE
  In unilateral biting or chewing, the working/balancing-side ratio (W/B-ratio) of masseter activities is inversely proportional to the jaw gape which was interpreted as a neuromuscular strategy to protect occlusion. This suggests that jaw separation is afferently perceived, raising the question how this perception might work. In related studies, isometric biting was exerted on rubber pieces that slightly yielded similar to compressed food in chewing. We hypothesized that minor jaw movements associated with this yielding are necessary to elicit a jaw gape-related control of relative activation in isometric biting.
  
  
  METHODS
  Surface electromyograms of masseter muscles were recorded bilaterally in 20 males during (a) unilateral chewing, (b) isometric biting on rubber pieces inducing jaw gapes of 5, 3, 2, 1, and 0.5 mm, and (c) isometric biting with teeth embedded in rigid splints causing gapes of 5 and 1 mm.
  
  
  RESULTS
  With rubber, the masseter W/B-ratio increased from 100 % (5 mm) to 166 % (1 mm) (p = 0.0003) whereas with the splint it increased just slightly to 112 % (p = 0.005). With 1 mm gape, W/B-ratios in splint biting were significantly smaller than in rubber biting or in chewing (p = 0.01).
  
  
  CONCLUSIONS
  We conclude that minor jaw motion preceding peak force in unilateral biting is necessary to create afferent sensory information that could elicit jaw gape-related activation of masseter muscles.
  
  
  CONCLUSIONS
  Demonstrating a condition under which jaw gape-related activation can lose its occlusion protecting effect, these findings might contribute to disclose the causes of craniomandibular disorders.
authors.affiliation: Department of Prosthodontics, University of Erlangen-Nürnberg, Dental Clinic 2, Glückstrasse 11, D 91054, Erlangen, Germany.
authors.forename: Thomas Riccardo
authors.initials: TR
authors.lastname: Morneburg
authors.forename: Sebastian
authors.initials: S
authors.lastname: Döhla
authors.forename: Manfred
authors.initials: M
authors.lastname: Wichmann
authors.forename: Peter Alfred
authors.initials: PA
authors.lastname: Pröschel
mesh_terms: D000328:Adult; D000344:Afferent Pathways; D001734:Bites, Human; D004576:Electromyography; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult